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DS2890V Datasheet(PDF) 7 Page - Dallas Semiconductor |
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DS2890V Datasheet(HTML) 7 Page - Dallas Semiconductor |
7 / 27 page DS2890 7 of 27 POWER With the charge pump off, the DS2890 can derive its power entirely from the 1-Wire bus by storing energy on an internal capacitor during periods of time when the 1-Wire bus is in a high state. During bus low times the device continues to operate from the energy stored on the internal capacitor; the capacitor is then recharged when the bus returns to a high state. This technique of operating entirely from the 1-Wire bus by powering from energy stored on an internal capacitor during bus low times in known as “parasite powered” operation. As an option, an auxiliary power source may be connected to the VDD power pin. The auxiliary power mode is appropriate for applications where device charge pump activation is necessary, the device may be temporarily disconnected from the 1-Wire bus, or bus low times may be very long. See Figure 5 for example configurations for both power modes. Figure 5. POWER SUPPLY CONFIGURATION OPTIONS (a) Auxiliary VDD Supply Configuration (b) 1-Wire Parasite Power Configuration POTENTIOMETER WIPER RESISTANCE AND CHARGE PUMP CONSIDERATIONS A simplified diagram of the DS2890 resistor array is shown in Figure 6. In this figure the rDS resistance of the wiper transistors in Figure 1 are modeled as wiper resistance RWIPER. The value of RWIPER varies with device configuration, operational state, and wiper terminal voltage. If an auxiliary external VDD supply configuration is used as shown In Figure 5a, the DS2890 charge pump may be enabled to reduce potentiometer wiper resistance. A consequence of enabling the charge pump is increased device power consumption. This increase is beyond the level that can be supported when operating in 1-Wire parasite power mode (see POWER section). Therefore if it is necessary to enable the charge pump in an application, the power supply configuration as shown in Figure 5a must be used. Figure 7 and Figure 8 are graphs of wiper resistance with the charge pump turned ON and OFF respectively. |
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